Mercaptan



mercaptans to disulfides. the sweetening of sour hydrocarbondistillates.

appreciably soluble in water. Ible copper salts which are suitable for'use' in the forma- 2,792,334 MERCAPTM oxrnATIoN PROCESS GarbisMeguerian, Park Forest, 111., assignor to Standand Gil(Iompany,'Chicago, 11h, a corporation of indiana 'No Drawing.Application May 26, 1%55,

" Serial No. 511,430

" Claims. (Cl. 196 -29) This invention relates to the catalyticoxidation of Also, the invention relates to t An object of invention isthe conversion of mercaptans to the corresponding disulfides bycatalyticoxidation,

Another object is a catalyst for the oxidation of mercaptans todisuliides. Still'anotherobject is a'process for the sweetening of sourhydrocarbon distillates by oxidation of the mercaptan content todisulfides in the presence of an oxidation catalyst. Yet another objectis the regeneration of aqueous alkaline mediums containing dissolvedmercaptans by oxidizing the mercaptans to disulfides, utilizing aparticular mercaptan oxidation catalyst.

' Other objects will become apparent in'the course of the detaileddescription of the invention. 7

"The'mercaptan oxidation catalyst utilized in the process of thisinvention consists of a complex formed by' the reaction ofawater-solublecopper salt with an alkylene polyamine, wherein the alkylene group isselected from the class consisting of ethylene and propylene. Themercaptan oxidation process is carried out bycontacting' an .aqueousalkaline medium containing the'mercap'tan to be converted withfree-oxygen in the presence of the copper-complex catalyst; theoxidation is carriedout at a temperature normally between about 40 F.and 200 F. Thedisulfides formed by the oxidation of the mercaptans aredecanted away'from the aqueous alkalinemedium or removed therefrom bywashingwith a solvent 'for the disulfides.

Sour pe-troletun'distillates are sweetened by contacting these with anaqueous alkaline medium containing a *catalytically effective amount ofthe de'fi'nedboppefipoly- .amine complex oxidation-catalyst and withfree-oxygen.

tion ofthe catalyst of the invention are cupric acetate, cupric bromate,cupric bromide, cupric chlorate, cupric chloride, 'cupric fluoride;cupric 3 'fiuosilicate, empir forma-te, cupric lactate, cupric nitrate,cup'ricsulfate, cup'ric methanesulfonate, cupric ethanesulfonate,cupricj benzene sulfonate, and cupric toluenesulfonate.'Tliesesalts'niay be "used either'in the anhydrous form ofihthe'hydrated form. The widely availableand"relativelyjhe g cupric'sulfate,'sold"as"bluevitriol,' i. 'e., 'CuSO iLSHQO, is a preferredwater-soluble copper salt.

' is an alkylene polyamine.

either ethylene or propylene.

2,792,334 Patented Mai; 14,19 5? The other component of the catalyst ofthis invention The alkylene group may be The alkylene polyamines maycontain one or more alkylene groups. It is preferred to utilize thosealkylene polyamines which are very water soluble and simultaneously ofrelatively low oil solubility. Examples of the alkylene polyamines whichmay be utilized in preparing the catalyst are ethylene diamine,diethylene triamine, triethylene tetramine, tetraethylene pentamine,propylene diamine, 'dipropylene triamine, tripropylene tetramine, andtetrapropylene pentamine. These alkylene polyamines may be utilized inc. p. grade,

the technical grade, or the commercial purities. The

"commerically available grade of diethylene triamine is a preferredsource of alkylene polyamine for use in the preparation of the oxidationcatalyst of this invention.

' The catalyst is prepared by reacting, in an aqueous medium, thewater-soluble copper salt and the alkylene 'aqueousmediumto complex allof the copper salt.

polya mine. Sufficient alkylene polyamine is added to the The particularamount of alkylene polyamine added is dependent uponfthe'particularallcylene polyamine being used. It appears that when utilizing ethylenediamine or propylene diamine' that thecomplex is tetrahedral andcontains two moles of the diamine and one gram atom of copperion. Moresimply, the complex can be prepared by slowly adding the polyamine to aconcentrated solution of copper salt in water until a blue precipitateappears. The presence of excess amine in the aqueous oxygen.

'm'edium'containing the complex salts out the complex in the form of ablue solid. The aqueous medium containing dissolved complex is a bluecolor. A complex essentially tree of excess polyamine is obtained bydecanting the aqueous medium from the precipitated blue solid and dryingthe solid at moderate temperature. Or a solution of complex in water ,ofknown concentration can be prepared by adding rpolyamine to an aqueoussolution of copper salt untihthe first appearance of precipitate; theprecipitate can be redissolved by the addition of water to thepreparation vessel. In any event, the presence of excessfpolyamine hasno deleterious effect on the catalytic "activit'y of thecopper-polyamine complex.

The mercaptan oxidation is carried out by bringing the mercaptanintosolution in aqueous alkaline medium.

This aqueous alkaline medium is preferably formed by the solutionof analkali metal hydroxide, such as sodium hydroxideandpotassium hydroxide,into water. Solutlons containing'calcium hydroxide or alkali metalcarbonates may-also be used. Efiective oxidation is also obtainableutilizing an alkylene poiyamine as the alkali r Th s i P $ibl qi n merap a p s or to sweeten hydrocarbon oils by contacting theo1l .et yl n .da ireicqnta ris me t r n a amly ticamount of copper-polyamine complexand freefl a i sf f elrnedium may contain substances wh imm r e, the;

lubility oi mercaptans in aqueous media. These substances which aremercaptan solubility p m ta't cu l f r tltq ss a ize may be amen the cancl ad iner a a th s p rp se; .hq

are? the... r19 .sc ilh i y p cmoters cf e t wi i omer a p yph sph s.mus earc d n rd t9 void d dat n of. the cat ys E am o q omma olubil ypromo e a a 'et an e hano a ylphs s si. at um oba rata t o ub eamine d.a sens am n s. .I .rnbre. c m asetubi y -n sar those Ph ns. e iveirompct o eum d st lates. For example; cresols derived from naphthas,and x l s uvsdt q f ea' iu o a kalm, me ia W are comnionly utili zed inthe pehose sol t1ons WhlCh troleum industry in the sweetening of sourhydrocarbon distillates by the use of free-oxygen and a mercaptanoxidation promoter. In general, at least enough aqueous alkaline mediumis utilized in the sweetening of a sour distillate to form a distinctseparate aqueous phase. More than thisv amount is commonly used, and ingeneral, between about and 100 volume percent of aqueous medium areused, based on sour distillate charged to the sweetening zone.

' oxygen is present to convert all of the mercaptans. Or,

when sweetening a hydrocarbon distillate, at least enough free-oxygen ispresent to produce an essentially sweet distillate. Since somesweetening normally takes place in the storage tanks subsequent to thesweetening operation,

it is not always necessary to complete the sweetening in the mercaptanoxidation zone.

The copper-polyamine complex catalyst of this invention is not degradedto any significant extent during the mercaptan oxidation or sweeteningprocess and may be reused apparently indefinitely. Further, the catalystdoes not need to be protected from oxidation by leaving in the aqueousalkaline medium some mercaptans unoxidized. Thus complete regenerationof mercaptide-containing aqueous medium is obtainable withoutsignificant loss of catalyst.

The mercaptan oxidation process is carried out at a temperature betweenabout F. and about 200 F. It is preferred to operate at the lowesttemperature that contacting time permits. In general, the lower thetempera ture of operation, the longer the contacting time needed toobtain complete oxidation of the mercaptan or sweetening of the sourdistillate. It is preferred to operate at a temperature between about 60F. and 90 F.

The mercaptan-containing aqueous alkaline medium may be prepared bydissolving mercaptans as such into the medium. To illustrate: When it isdesired to prepare high purity dimethyl disulfide from methyl mercaptan.Or the mercaptans may be obtained by contacting a sour hydrocarbondistillate with an aqueous caustic solution. By this oxidation of themercaptans in the aqueous alkaline medium, it is possible to recover thedisulfides produced.

On the other hand, when it is simply desired to remove the malodorousmercaptans from a sour hydrocarbon distillate by converting them to thebland smelling disulfides, the mercaptan oxidation process, i. e.,sweetening process, is carried out by contacting the sour distillatewith catalyst containing aqueous alkaline medium in the presence offree-oxygen until the mercaptans have been essentially completelyconverted to disulfides. The sweet distillate removes the disulfidesfrom the aqueous medium so that the sweet distillate contains disulfidesinstead of mercaptans. The aqueous medium may then be separated from thesweet distillate and used to treat another batch of sour distillate. Itis to be understood that the sweetening of a sour distillate may bebatchwise or continuous,

utilizing the techniques well known in this art.

The aqueous alkaline medium contains at least a cat alytically elfectiveamount of the copper polyamine complex catalyst. In general, the aqueousalkaline medium will contain between about 0.02 and 1 weight percent,calculated as copper, of the catalyst. More usually the catalyst contentwill be between about 0.1 and 0.2 weight percent as copper. The largeamounts of catalyst content have a favorable effect on the rate ofmercaptan oxidation. The catalyst may be utilized for the sweetening ofsubstantially any hydrocarbon distillate which contains significantamounts of mercaptans, i. e., is sour to the doctor test. The sourhydrocarbon distillate may be of petroleum origin, or it may be a coaltar distillate. The sour petroleum distillates may be virgin distillatesor may be derived from thermal or catalytic conversion processes. Theprocess is particularly suitable for sweetening of stocks which boilbelow about 700 F. Examples of sour petroleum distillates which aresuitable feeds to the sweetening process are virgin naphtha, thermallycracked naphtha, catalytically cracked naphtha, kerosene, diesel fuel,heater oil, and furnace oil.

The results obtainable with the process of the invention are illustratedby the following working examples. These examples are not to beconsidered as limiting the scope of the invention.

Two types of catalyst polyamine complexes were pre pared and utilized.One complex was prepared by dissolving one gram of cupric sulfatepentahydrate in 5 ml. of water and 2 ml. of technical grade ethylenediamine was added to the salt solution. The addition of more ethylenediamine to the solution resulted in the precipitation of a blue solid.The other solution was prepared by adding one gram of cupric sulfatepentahydrate to 8 ml. of water and 7 ml. of diethylene triamine. Theaddition of more polyamine caused the precipitation of a blue solid. Inall cases, the copper polyamine complex containing aqueous media weredeep blue in color. To prepare the catalyst containing aqueous alkalinemedia, portions of the preformed complex solutions were added to theaqueous alkaline media.

Tests were carried out on the oxidation of mercaptide solutions preparedby aqueous caustic contacting of sour cracked naphtha. Tests werecarried out on sweetening of sour distillates using: a virgin naphthaboiling over the range of about 100 F. to 325 F.; a thermally crackedheavy naphtha boiling over the range of about 200 F. to 400 F.; a sourcatalytically cracked naphtha boiling over the range of about 200 F. to400 F.; a sour heater oil boiling over the range of about 325 F. and 550F.

TEST 1 In this test, a rich solution prepared by the contacting of asour thermally cracked naphtha with an aqueous caustic solutioncontaining about 12 weight percent sodium hydroxide and about 10 volumepercent of petroleum cresols was regenerated by treatment at varioustemperatures. The rich mercaptide-containing solution was placed in avessel and heated to the desired temperature of regeneration; air wasintroduced into the vessel while the vessel was being stirred by apropeller stirrer. At

each temperature the contacting was maintained for 10 minutes. At eachtemperature solution with and without catalyst was contacted forpurposes of comparison. The

catalyst utilized in this test was a copper-diethylene triamine complexand the catalyst-containing rich solution contained 0.5 weight percentof copper. The activity of the catalyst was determined by measuring theamount of mercaptan sulfur oxidized as milligrams. The results of thistest are set out in Table A below.

Runs 1 and 2 show that the catalyst-containing solution converted morethan 4 times as much mercaptan as the non-catalyzed solution. It ispointed out that petroleum cresols are generally considered to be fairmercaptan oxidation catalysts in their own right. The conversion in Runs4 and 6 as compared with 3 and 5 are not as favorable owing tothe factthat the higher temperature of operation in these runs favors the lessactivesystem more. than it did the catalyst containing system. Theseruns show that the copper-diethylene triamine complex, is an extremelyeffective mercaptan oxidation catalyst.

TEST 2 In this test, virgin naphtha having a mercaptan number of 19.9(mg, of mercaptan sulfur per 100 ml. of naphtha) was sweetened. 100 ml.of ethylene diamine containing about 30 volume percent of water andsufiicient copperethylene diamine complex to introduce 0.07 weightpercent. of copper into the solution was contacted with 250 ml. of thevirgin naphtha. At 70 F. the naphtha was sweetened in minutes. Theaqueous phase was decanted from the sweet naphtha and used to sweetenanother batch of sour naphtha. This was repeated until 4' batches ofsour naphtha had been sweetened. In each instance, the sweetening timewas 10 minutes. This test shows that alkylene polyamine-alk-alinesolution is an eifective aqueous alkali medium and also shows that thealkaline medium can be reused several times without loss of catalystactivity.

TEST 3 In this test, the sour hydrocarbon distillate was a West Texasheater oil having a mercaptan number of 50. The aqueous alkalinesolution consisted of 30 ml. of 20% NaOH, 20 ml. of commercial ethylenediamine, and 5 ml. of copper-diethylene triamine complex solution. Theaqueous alkaline solution contained 0.4 weight percent of copper. Thecontacting was carried out at a temperature of 110 F. and the heater oilwas sweet after 35 minutes. The color of the sweet heater oil was waterwhite. This test shows that the process of the invention is eltective onsweetening what is generally considered to be the most refractory typeof stock present in commercial refinery operations, namely a very highsulfur, high boiling distillate.

TEST 4 In this test, a West Texas heater oil having a mercaptan numberof 87 was the feed. The aqueous alkaline solution contained 40 volumepercent of ethylene diamine and the remainder 20% sodium hydroxide-watersolution. The aqueous medium contained copper-diethylene triaminecomplex equivalent to 0.2 weight percent of copper. At a temperature of95 F. a sweet oil was produced in 65 minutes.

TEST 5 In this test, the possible carryover of copper with the sweetdistillate was investigated. The sour distillate was a thermally crackedheavy naphtha which had been extracted with aqueous caustic-cresylatesolution to a mercaptan number of 5. The sour thermally cracked naphthawas contacted at 75 F. with an aqueous alkaline solution containing 0.1weight percent as copper of the copperethylene diamine catalyst. Thenaphtha was sweet in about 6 minutes. The sweet naphtha was inhibitedwith 2 pounds per 1000 barrels of commercial N--Ndi-secbutyl-p-phenylene diamine and the ASTM induction period test runon the inhibited naphtha. The induction period was 145 minutes. Anothersample of the sweet oil was inhibited with 2 pounds per 1000 barrels ofthe phenylene diamine inhibitor and 2 pounds per 1000 barrels ofcommercial metal deactivator. The induction period of the metaldeactivator containing sweet naphtha was 145 minutes. The fact that themetal deactivator did not improve the induction period shows that nocopper had been carried over into the sweet oil from the sweeteningzone.

TEST 6 In this test, the effect of concentration of catalyst in theaqueous solution on the sweetening time was studied. The sour distillatewas a thermally cracked heavy naphtha having a mercaptan number of 7.The contacting temperature was 75 F.; the catalyst was acopper-diethylene triamine complex; the aqueous solution containedpetroleunr cresols in, addition to sodiumhydroxide. The concentration ofcatalyst calculated as copper and the corresponding time in minutesneeded to produce a sweet naphtha is set out in Table -B below.

These data show that the, sweetening rate is increased five-fold hy' thepresence of only 0.2 weight percent of copper as compared with thesolution containing no copper catalyst.

TEST 7 In this test, the. eifect of sweetening on the color stabilityofthe sweet distillate was studied. The feed. was.

a thermal naphtha having a mercaptan number of 7 and a color of +14Saybolt. The test was carried out at F. The aqueous alkaline solutioncontained 12 volume percent of petroleum cresols and 13 weight percentof sodium hydroxide. In one run, cupric chloride was dissolved in theaqueous solution and the sour naphtha sweetened. In another run,copper-ethylene diamine complex was dissolved in the aqueous solutionand the oil sweetened. In each run, 0.4 weight percent of copper waspresent. The sweetening time in each run was about 6 minutes. The sweetoil was water washed to remove occluded aqueous solution and then wasmaintained at about 72 F. for 24 hours exposed to the atmosphere. Thecolor of the oil after the 24 hour exposure was determined. The resultsof these runs are set out in Table C below.

These runs show that the copper-polyarnine complex catalyst of thisinvention has very little deleterious effect on the color stability ofsuch an insensitive material as a thermally cracked naphtha. Althoughthe cupric chloride catalyst i very effective in sweetening, Run No. 7show that the sweet naphtha is extremely unstable with respect to color.

The above working examples show that the copperalkylene polyaminecomplex is an extremely active catalyst for the oxidation of mercaptansto the corresponding disulfides and that the catalyst has no significantdeleterious effects on oil sweetened utilizing the catalyst and alsothat the catalyst-containing solution may be reused many times withoutloss in oxidation activity.

Thus having described the invention, what is claimed 1. A process forconverting mercaptans to disulfides which comprises contacting anaqueous alkaline medium containing a mercaptan with free-oxygen at atemperature between about 40 F. and 200 F., in the presence of amercaptan oxidation catalyst consisting of the complex formed by thereaction of a water-soluble copper salt and an alkylene polyaminewherein the alkylene group is selected from the class consisting ofethylene and propylene.

2. The process of claim 1 wherein said polyamine is ethylene diamine.

3. The process of claim 1 wherein said polyamine is diethylene triamine.

4. The process of claim 1 wherein said polyamine is dipropylenetriamine.

p 5. The process of claim 1 wherein said salt is cupric sulfate. 6.' Theprocess of claim 1 wherein said salt is cupric chloride.

7. The process of claim 1 wherein said temperature is between about 60F. and 90 F.

8. The process of claim 1 wherein said catalyst is present in an amountof between about 0.02 and 1 weight percent, as copper, based on aqueousalkaline medium. I 9. A process for sweetening sour hydrocarbondistillate which comprises contacting said distillate, at a temperaturebetween about 40 F. and 200 F., with an amount of an aqueous alkalinemedium sufiicient to form a distinct, separate aqueous phase, whichmedium contains between about 0.02 and 1 weight percent, as copper, of acatalyst formed by the reaction of a water soluble copper salt and analkylene polyamine where the alkylene group is selected from the classconsisting of ethylene and propylene, and with free-oxygen in an amountat least sufiicient to convert essentially all of the mercaptans in saiddistillate to disulfides, for a time at least sufiicient to essentiallysweeten said distillate and separating an essentially sweet oil from anaqueous phase.

10. The process of claim 9 wherein said temperature is between F. and F.

11. The process of claim 9 wherein the catalyst content is between about0.1 and 0.2 weight percent.

. 12. The process of claim 9 wherein said distillate is a virginpetroleum naphtha.

13. The process of claim 9 wherein said distillate is a crackedpetroleum naphtha.

14. The process of claim 9 wherein said distillate is a heater oil.

15. The process of claim 9 wherein said distillate is a kerosene.

References Cited in the file of this patent UNITED STATES PATENTSFetterly Dec. 9, 1947 Krause et a1. Dec. 22, 1953

1. A PROCESS FOR CONVERTING MERCAPTANS TO DISULFIDES WHICH COMPRISESCONTACTING AN AWUEOUS ALKALINE MEDIUM CONTAINING A MERCAPTAN WITHFREE-OXYGEN AT A TEMPERATURE BETWEEN ABOUT 40* F. AND 200* F., IN THEPRESSURE OF A MERCAPTAN OXIDATION CATALYST CONSISTING OF THE COMPLEXFORMED BY THE REACTION OF A WATER-SOLUBLE COPPER SALT AND AN ALKYLENEPOLYAMINE WHEREIN THE ALKYLENE GROUP IS SELECTED FORM THE CLASSCONSISTIN OF ETHYLENE AND PROPYLENE.
 9. A PROCESS FOR SWEETENING SOURHYDROCARBON DISTILLATE WHICH COMPRISES CONTACTING SAID DISTILLATE, AT ATEMPERATURE BETWEEN ABOUT 40* F. AND 200* F., WITH AN AMOUNT OF ANAQUEOUS ALKALINE MEDIUM SUFFICIENT TO FORM A DISTINCT, SEPARATE AQUEOUSPHASE, WHICH MEDIUM CONTAINS BETWEEN ABOUT 0.02 AND 1 WEIGHT PERCENT, ASCOPPER, OF A CATALYST FORMED BY THE REACTION OF A WATER SOLUBLE COPPERSALT AND AN ALKYLENE POLYAMINE WHERE THE ALKYLENE GROUP IS SELECTED FROMTHE CLASS CONSISTING OF ETHYLENE AND PROPYLENE, AND WITH FREE-OXYGEN INAN AMOUNT AT LEAST SUFFICIENT TO CONVERT ESSENTALLY ALL OF THEMERCAPTANS IN ESSENTIALLY SWEETEN SAID DISTILLATE AND SEPARATING ANESSENTIALLY SWEET OIL FROM AN AQUEOUS PHASE.